Tensile properties of compression-molded whey protein sheets: Determination of molding condition and glycerol-content effects and comparison with solution-cast films

Transparent glycerol (Gly)-plasticized whey protein isolate (WPI) sheets could be formed from Gly-WPI mixtures using compression molding, demonstrating that such mixtures display flowability and fusion behavior under certain conditions. The effects of glycerol content (GC), molding temperature and molding pressure on the tensile properties of the transparent compression-molded WPI sheets were studied, and the properties were compared to those of films produced using the solution-casting method. Compression-molding temperature and pressure did not significantly affect sheet stiffness (elastic modulus, EM), strength (tensile strength, TS) or extension (% elongation, %E) (p > 0.05). Increasing the GC of compression-molded sheets decreased EM and TS, but had little effect on %E. The values of TS and %E of compression-molded WPI sheets with 40–50% GC were greater than those of solution-cast WPI films with 45% GC. These results indicate the possibility that Gly-WPI mixtures can be extruded into films for formation of edible or biodegradable wraps or heat-sealed pouches.